1. Field of the Invention
The present invention relates to a motion detection device for use in a photographic device, such as a camera, to detect motion, such as vibration or shake caused by hand tremor. More particularly, the present invention relates to a motion detection device, suitable for use in a camera motion compensation system, which includes a motion sensor to detect motion and which accurately determines an integration constant as a reference value for control when an integration device performs time integration of the output of the motion sensor.
2. Description of the Related Art
Camera shake detection devices to detect camera shake are known. For example, photographic devices, such as a still camera, having a camera shake detection device have been proposed. In the conventional type of camera, the camera shake detected by the camera shake detection device is used to compensate for image blur caused by the camera shake. Specifically, the camera shake detection device outputs a detection signal which is used to control movement of a camera shake compensation lens, which is a part of a photographic lens, in a direction almost perpendicular to the optical axis, thereby compensating for image blur caused by the vibration of the camera at the time of a photographic operation.
A camera having an anti-vibration optical system for performing a conventional shake compensation operation is disclosed in Japanese Laid-Open Patent Publication No. H4-76525. The camera disclosed in Japanese Laid-Open Patent Publication No. H4-76525 consists of a camera shake compensation lens which is moveable in a plane perpendicular to the optical axis; a frame member to hold the camera shake compensation lens; a plate member to hold the frame member; four wires attached to the plate member; a main body to support the four wires; an actuator consisting of a winding coil, a yoke, and a permanent magnet to drive the camera shake compensation lens both vertically and horizontally; a light emitting element; a photosensor; and a position detection device to detect the position of the camera shake compensation lens.
The operation of the conventional camera shake compensation device will be described below with reference to FIG. 5, which is a block diagram of the conventional camera shake compensation device. As shown in FIG. 5, angular velocity sensor 10 detects camera shake. The angular velocity sensor 10 is, for example, a piezoelectric vibration type angular velocity sensor to detect the colioli force and to monitor the vibration of the camera. The output of the angular velocity sensor 10 is input to an integration section 40 to perform time integration of the output of the angular velocity sensor 10. The time integrated output of the angular velocity sensor 10 is converted into a shake angle of the camera, and then the integration section 40 converts the shake angle into target drive position information which is input to a servo circuit 100. A position detection device 120 monitors the movement of the camera shake compensation lens and feeds position information back to the servo circuit 100. The servo circuit 100 then calculates a difference between the target drive position information and the position information of the camera shake compensation lens, and transmits difference signals to an actuator 110 to drive the camera shake compensation lens according to the target drive position information. The actuator 110 drives the camera shake compensation lens within a plane that is almost perpendicular to the optical axis.
Conventional camera shake compensation devices require an integration constant which serves as a reference value for control when the integration section 40 performs time integration of the output of the angular velocity sensor 10. A method of calculating the integration constant is disclosed in, for example, FIGS. 17 and 18 of Japanese Laid-Open Patent Publication No. H4-211230.
A camera shake sensor of the camera shake compensation device disclosed in Japanese Laid-Open Patent Publication No. H4-211230 includes an angular velocity sensor to detect the colioli force; a drift element detection section, consisting of a central processing unit (CPU) and a memory, to calculate a mean value of the output of the angular velocity sensor which is sampled from a present time up to a designated time; and a subtractor to eliminate drift elements by subtracting the mean value from the output of the angular velocity sensor and to output the subtraction value thereof.
According to Japanese Laid-Open Patent Publication No. H4-211230, the output from the angular velocity sensor is entered to the drift element detection section every 10 milliseconds (ms), and fifty (50) outputs are entered every 0.5 seconds (10 ms.times.50). A calculated mean value for the fifty (50) outputs (hereinafter referred to as "mean 1") is stored in the memory of the drift element detection section. The "mean 1" is calculated twenty (20) times for 1000 outputs of the angular velocity sensor and entered in the memory of the drift element detection section after ten (10) seconds (0.5 seconds.times.20) have elapsed. Consequently, after ten (10) seconds from the start, the mean value for 1000 outputs (50.times.20) of the angular velocity sensor can be calculated.
In operation of the above-described conventional camera shake compensation device, it is necessary to determine the integration constant when integrating the output signal from the angular velocity sensor since the output signals from the angular velocity sensor are first integrated, and then converted into angular displacement information to be processed. Generally, the output from the angular velocity sensor when the camera is static (hereinafter referred to as "omega zero") is used as the integration constant.
However, photographic devices, such as a camera, normally vibrate due to the shaking of a photographer's hands when taking a photograph while manually holding the photographic device. Under these conditions, it is impossible to directly measure the output of the angular velocity sensor when the angular velocity sensor is static. Therefore, it is necessary to compute the omega zero based on the output signals of the angular velocity sensor with added vibration caused by the shaking of hands.
FIGS. 6A and 6B are graphs illustrating angular velocity and angular displacement, respectively, when omega zero has been accurately computed with a conventional camera shake compensation device. FIGS. 7A and 7B are graphs of angular velocity and angular displacement, respectively, when omega zero has been inaccurately computed with a conventional camera shake compensation device. More particularly, FIGS. 6A and 7A illustrate the angular velocity signal output from the angular velocity sensor. FIGS. 6B and 7B illustrate the angular displacement signal obtained from the angular velocity signal. In order to simplify the explanation below, it is assumed that the camera shake is entered as a sine wave and the omega zero is zero (0).
As shown in FIG. 6A, the center of the amplitude of the angular velocity signal is zero, and it is assumed that the value of omega zero is correctly attained at zero. Providing that the integration constant is the omega zero shown in FIG. 6A, an integration computation for the angular velocity attains the angular displacement signal shown in FIG. 6B. The angular displacement signal is accurately calculated when the angular velocity signal is integrated by applying the accurately obtained omega zero as an integration constant. Therefore, camera shake compensation can be achieved with a high degree of precision when the camera shake compensation lens is controlled using an angular displacement signal that has been accurately calculated.
On the other hand, as shown in FIG. 7A, the center of the amplitude of the angular velocity signal is not zero. As a result, the value of the calculated omega zero is not correctly attained at zero, and, instead, an offset value is applied. By performing the integration computation with the use of an incorrect omega zero value as an integration constant, an angular displacement signal with an added linear gradient is obtained, as shown in FIG. 7B. Therefore, if an incorrect omega zero value is used as an integration constant, the angular displacement signals cannot be accurately calculated. If the camera shake compensation lens is controlled with such an inaccurately calculated angular displacement signal, the camera shake compensation lens drifts while vibrating and camera shake compensation cannot be executed with a high degree of precision, thereby possibly worsening the image blur. Thus, precisely computing omega zero is an essential factor in performing shake compensation.
As discussed above, FIGS. 17 and 18 of Japanese Laid-Open Patent Publication No. H4-211230 disclose a method of computing the omega zero known as the movement average method. However, the movement average method disclosed in Japanese Laid-Open Patent Publication No. H4-211230 requires some time to accumulate the data to calculate the average. For example, when using the movement average computation method disclosed in Japanese Laid-Open Patent Publication No. H4-211230, omega zero is computed by calculating the mean 1 twenty (20) times for fifty (50) data inputs obtained every ten (10) ms. Thus, it takes ten (10) seconds (10 ms.times.50.times.20) from the beginning of computation to the output of omega zero. As a result, omega zero cannot be output by the conventional camera shake detection device for the first ten (10) seconds after activating the camera shake detection device.
For example, if the conventional camera shake detection device begins the computation of omega zero as a half-push switch (i.e., a photographic operation ready switch) of a camera is switched on by a photographer, camera shake compensation cannot be executed for the first ten (10) seconds after the computation has begun. As a result, a problem occurs in that a shutter opportunity could be missed during the time required to calculate omega zero, before camera shake compensation becomes possible.
Furthermore, if the number of samplings for the computation of the mean is decreased in order to expedite the output of omega zero, another problem occurs in that omega zero cannot be accurately detected, thereby reducing the effectiveness of the camera shake compensation or worsening the image blur.